The augmentation of the acute motor activity response to cocaine, which occurs with repeated, intermittent administration, is termed behavioral sensitization. In humans, sensitization is manifest as stimulant-induced psychosis that has an etiology similar to the paranoid psychoses of schizophrenia. An understanding of the mechanisms involved in the development of sensitization could be important in developing more effective pharmacological treatments for stimulant-induced psychosis as well as the paranoid psychoses of schizophrenia. It has been suggested that changes in the tonic inhibitory regulation of dopamine neurons located in the ventral tegmental area (A10 region) may be important in the development of behavioral sensitization. One focus of the project will therefore be to continue to study the effects of intra-A10 administration of drugs, which may alter the tonic inhibition of dopamine neurons, on the acute and the sensitized motor-stimulant responses to cocaine as well as the cocaine-induced increases in dopamine release in the nucleus accumbens (a terminal site of the A10 region). Dopamine release will be monitored by in vivo microdialysis. In other models of sensitization in the nervous system, an increase in protein kinase C (PKC) activity has been correlated with the augmented response to a stimulus. Thus, a second focus of the project will be to analyze behaviorally and neurochemically the role of PKC in cocaine-induced sensitization. The behavioral PKC studies will examine the effects of intra-A10 injection of PKC activators and/or inhibitors on the acute and sensitized behavioral responses to cocaine. These studies will be coupled with in vivo microdialysis to determine whether behavioral changes are correlated with changes in dopamine release in the nucleus accumbens. The neurochemical PKC studies will 1) determine the effects of acute and daily cocaine administration on total PKC activity by use of a histone phosphorylation assay, 2) determine whether changes in PKC activity are specific to a particular isozyme of PKC by use of immunoblot procedures and 3) determine whether changes in PKC activity are expressed at the genetic level by use of northern blot analysis of mRNA levels for PKC. Since other dopamine systems have been implicated in sensitization, the neurochemical studies will be conducted on tissue samples from not only the mesolimbic dopamine system, but also the mesocortical and nigrostriatal dopamine systems. The long term goal of this project is to determine whether cocaine-induced sensitization is related to changes in the tonic inhibition of dopamine neurons and whether these changes are related to an increase in PKC activity and a phosphorylation of proteins involved in inhibitory signal transduction.